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kotlinlang

I'm curious why CMP team needs to create a separate previews library for multiplatform, what are the technical challenges for using the Android previews?

I guess you want to see each platform's real renderer implementation result. Get the closest to what would happen in each platform.
You have a good point anyway. You can then blindly  assume/trust compose will behave the same and it will open many possibilities. Like even using a webpage application to create your Composable, no more Fleet for this purpose.

The best thing about Android previews is the configurations and the incremental compilation. It's so fast and you can see changes immediately.
Also the IDE support is so much better. I think that they can use the same previews panel on multiplatform.